392 COMPARATIVE ANATOMY 



As the subclavian artery passes out from under the clavicle towards 

 the arm it becomes the axillary artery. In the five inches of its length 

 the axillary artery gives off the superior thoracic, thoraco-acromial, 

 lateral thoracic, subscapular, anterior circumflex humeral, and posterior 

 circumflex humeral arteries to the muscles of the shoulder and chest. 

 Continuing into the arm the axillary artery becomes the brachial artery 

 which extends to the elbow and there divides into radial and ulnar arteries. 

 Its branches supply the bone muscles and skin of the upper arm. The 

 radial and ulnar arteries are the chief arteries of the forearm; those of 

 the hand are the volar and digital arteries, their branches supplying chiefly 

 muscles and skin. The pulse is usually taken from the radial artery in the 

 wrist. 



The thoracic portion of the dorsal aorta extends from the aortic arch 

 at the level of the fourth thoracic vertebra to the level of the twelfth 

 thoracic vertebra, where it passes through the diaphragm and becomes 

 the abdominal aorta. The chief branches of the thoracic aorta are ten 

 pairs of intercostal arteries, which not only supply the intercostal muscles 

 but also the vertebral canal and the skin of the thoracic region. Small 

 arteries are given off to the bronchi, lungs, esophagus, and mediastinum. 



The abdominal aorta extends from the diaphragm to the fourth lumbar 

 vertebra. As it passes downwards it gives off in succession right and 

 left inferior phrenics, celiac, right and left middle adrenal, right and left 

 first lumbar, superior mesenteric, right and left renal, right and left 

 internal spermatic, right and left second lumbar, inferior mesenteric, 

 right and left third and fourth lumbar, right and left common iliac, and 

 middle sacral arteries. Of these the phrenics and lumbars are parietal 

 in distribution while the remainder, except the iliac and sacral, are 

 visceral. 



The right and left inferior phrenic arteries supply the diaphragm and 

 adrenals. The lumbar arteries supply the lumbar vertebrae and the 

 lumbar muscles. One branch anastomoses with the renal artery. The 

 celiac artery divides into three chief branches, the left gastric, the hepatic, 

 and splenic (lienal) arteries. The left gastric artery supplies the lesser 

 curvature of the stomach and the lower part of the esophagus. The 

 hepatic artery supplies the liver, duodenum, pancreas, and the right 

 half of the greater curvature of the stomach. The third branch of the 

 celiac is the splenic which, as its name implies, supplies the spleen and also 

 the pancreas and the stomach wall. 



The superior mesenteric artery extends for most of its course in the 

 mesentery and gives off five chief branches, inferior pancreatico-duodenal, 

 intestinal, ileo-colic, right colic, and middle colic. The inferior pan- 

 creatico-duodenal artery anastomoses with the superior pancreatico- 

 duodenal artery, a branch of the hepatic. The intestinal arteries supply 



